Inverted tooth chains have long been used to transmit power and motion between shafts in automotive applications and they are conventionally constructed as endless chains with ranks or rows of interleaved inside link plates each having a pair of toes, and having aligned apertures to receive pivot pins to join the rows and provide articulation of the chain as it drivingly engages the sprocket teeth either at the inside flanks or at the outside flanks of the link plate teeth at the onset of meshing with the driving and driven sprockets. Although both meshing styles have been used for automotive timing drives, inside flank engagement is more commonly used for these drives. Guide link plates are located on opposite sides of alternating rows of inside link plates in order to position the chain laterally (axially with respect to the axis of rotation) on the sprockets.
FIG. 1 shows a conventional inverted tooth chain drive system 100 with an inverted tooth chain 110 in meshing contact with drive sprocket 150 as the sprocket rotates clockwise about its center X (axis of rotation), and another sprocket not shown. The sprocket 150 includes a plurality of teeth 160 each having an engaging flank 162 and the teeth are symmetrical about their tooth centers TC and are all substantially identical. The sprocket 150 has a total of N teeth, and the tooth centers TC are spaced A degrees from each other, where A=360/N. The illustrated tooth flanks 162 have an involute form, but can alternatively comprise a radial arc shape and/or comprise or be defined by a straight-sided profile (flat). The outside diameter OD and root diameter RD define the outer and inner radial limits of the tooth flanks. As shown in FIG. 1, the chain link plates do not contact either the outside diameter OD or the root surface 165 as defined by root diameter RD. The teeth 160 are identical to each other and are evenly spaced circumferentially from each other, with tooth centers TC located every 360/N degrees, where N is the total number of teeth.
FIG. 2A illustrates first and second rows 130a,130b of chain 110. The conventional inside link plates 130 of each row have toes 138 which are each defined by inside flanks 135 and outside flanks 136 interconnected by a tip 137 defined by a radius and/or other surface. In the illustrated embodiment, outside flanks 136 are straight-sided and the inside flanks 135 have a convexly arcuate form and are joined by a crotch 134. In particular, the inside flanks 135 of each link 130 are defined by a radius R that preferably blends into the tip 137 of the relevant toe 138 and into the crotch 134 at the opposite end. When the chain is pulled straight as shown in FIG. 2A (it's nominal orientation as it moves into engagement with the sprocket 150 from the span during use), the inside flanks 135 project outwardly from the adjacent overlapping outside flanks 136 of preceding link row by a projection height λ, thereby permitting the inside flanks 135 of a row 130a,130b to make initial meshing contact with an engaging flank 162 of a sprocket tooth 160 at the onset of meshing. FIG. 2B is a plan view of the chain 110 and shows a standard chain lacing having rows 130a,130b,130c, etc. of interleaved inside links 130, with successive rows pivotally interconnected by pivot pins 140 or rocker-type joints (the term “pin” is intended to encompass a simple pin or a rocker joint or any structure that pivotally joins successive link rows 130a,130b,130c. Other inside link lacings having stacked inside links 130 across a row are also commonly used.
Referring again to FIG. 1, the chain 110 approaches the drive sprocket 150 substantially along the tangent line TL (at the centers of the chain pins 140) in a taut strand and meshing occurs as the chain inside links 130 of rows 130a,130b,130c collide with an engaging flank tooth face 162. When the chain 110 moves into the wrap of the sprocket and is fully meshed with the sprocket 150, the centers of the pins 140 travel along and define a circular path referred to as the pitch diameter PD.
Referring now to FIG. 3, which is an enlarged view of FIG. 1, link plate rows 130a and 130b of chain 110 are shown at the instant of simultaneous meshing contact with the engaging flank 162 of tooth 160b, i.e., in a state between initial contact with only the leading inside flanks 135 of link row 130b and transition to engagement only with trailing outside flanks 136 of a preceding link row 130a. Link row 130b is making leading inside flank meshing contact IF with tooth flank 162 and link plate row 130a has just rotated into trailing outside meshing contact OF to affect this simultaneous meshing contact. As sprocket 150 continues its rotation, inside flanks 135 of link plate row 130b will separate from contact with the engaging flank 162 of tooth 160b and will continue to further separate until the sprocket rotation articulates link plate row 130b to its chordal position in the sprocket wrap, which occurs when its trailing outside flanks 136 come into meshing contact OF with engaging flank 162 of tooth 160c. It should be noted that the transition from leading inside flank contact of link row 130b to trailing outside flank-to-tooth contact of preceding link row 130a, as described, is not believed to contribute in any significant measure to the meshing impact noise levels in that the initial meshing and driving engagement of the chain links with the sprocket teeth 160 occur at the inside flanks 135 at the onset of meshing, and it is this initial chain-sprocket meshing impact that is believed to be the major noise source. The meshing cycle for a link row starts with initial meshing contact IC and ends when the link row articulates to, and is seated at, its chordal position in the sprocket wrap, having only trailing outside flank contact OF.
It is important to note that initial contact IC between the chain 110 and sprocket 150 is always inside flank meshing contact IF. Inside flank contact IF (see FIG. 3) continues even after the initial contact IC, as shown in FIG. 4, since initial contact by definition occurs at the instant when the leading inside flanks 135 of a chain row first make inside flank meshing contact IF with a sprocket tooth 160, and the inside flanks 135 of the chain link row remain substantially in contact with the engaging flank 162 of a sprocket tooth 160 until the meshing transition to the outside flank meshing OF occurs, following which the inside flanks 135 will separate from contact with the tooth face 162.
Referring again to FIG. 4, the drive sprocket 150 has continued to rotate in a clockwise direction, relative to the position shown in FIG. 3, until link plate row 130c is at the onset of initial meshing contact IC with sprocket tooth 160c. The angle θ is shown to be the angle between a base reference line VL originating at the sprocket center (axis of rotation X) and passing through the sprocket teeth at the 12 o'clock (i.e., top-dead-center) position, and another reference line CL originating at the sprocket center X and passing through the initial meshing contact point IC at tooth 160c, and this is the angle at which initial meshing contact IC will occur between the leading inside flanks 135 of a chain row 130a,130b, etc. and any tooth 160 in the symmetrical drive sprocket 150, i.e., at the instant of initial contact between a row of chain link plates 130 and a sprocket tooth 160, the angle θ will always be defined as the angle between the base reference line VL and the second reference line CL extending between the sprocket center and the initial meshing contact point IC.
Chain-sprocket impact at the onset of meshing is the dominant noise source in chain drive systems and it occurs as the chain links leave the span and collide with a sprocket tooth at engagement. Transverse vibration in the “free” or unsupported span as the chain approaches the sprocket along the tangent line TL will add to the severity of the meshing impact. The resultant impact noise is repeated with a frequency generally equal to that of the frequency of the chain meshing with the sprocket. Many attempts to reduce the noise associated with inverted tooth chain drives have been related to the chain-sprocket meshing phenomenon. It is well known in the art that an inverted tooth chain having inside flank meshing will generally provide a smooth chain-sprocket engagement. The noise generation associated with chain-sprocket meshing impact, however, still occurs for inside flank meshing contact and it is an object of the present invention to reduce these noise levels.